This invention relates to improved apparatus and methods for jacking two members axially relative to one another. Certain aspects of the invention are especially useful for leveling a marine platform jacket, and the invention will therefore be described primarily as applied to that use.
Marine platforms for off-shore well drilling and other similar uses are normally supported on a structure referred to as a `jacket`, forming a framework which projects downwardly into the water and rests on the sea bed. Piles are driven downwardly through tubular legs and/or tubular pile guides forming portions of the jacket, and into the earth formation beneath the water, to rigidly secure the jacket and platform in fixed positions. Grout is filled into spaces radially between the piles and the surrounding tubular portions of the jacket, and allowed to set, to lock the jacket against displacement relative to the piles. If the platform is not initially level when the jacket comes to rest on the sea bed, one side of the jacket may be jacked upwardly relative to the other side to level the platform before the grouting operation.
There is disclosed in copending U.S. patent application Ser. No. 06/227,735, now U.S. Pat. No. 4,367,056 entitled "Marine Platform Jacket Jack", filed Jan. 23, 1981 by Padmasiri D. Seneviratne a jacking mechanism which can be utilized for jacking a tubular leg or pile guide of a marine platform jacket upwardly relative to a pile extending through that tubular member to attain the above discussed platform leveling action. The jacking mechanism includes a gripping unit receivable about a pile or other member and preferably having tapered wedging slips which are cammed against the pile in a relation supporting the gripping unit against movement downwardly relative to the pile. Power actuated means desirably taking the form of piston and cylinder mechanisms are then operable to pull the tubular member about the pile upwardly relative to the gripping unit to thereby jack the platform to a proper level condition. In the arrangement of that prior application, the upward force is applied to the tubular member through a second slip-type gripping unit.